Glenn Beck nails it

As John has noted, America remains unclear about President Obama’s religious affiliation. Thus, in a Pew Research survey, 43 percent (a plurality) said they don’t know which religion Obama practices.
John has offered some good explanations for this uncertainty, especially the misperception that Obama is a Muslim. But I think it is Glenn Beck who has the best explanation for why so many Americans don’t identify Obama as a Christian. Beck told Fox News that, “Obama is a guy who understands the world through liberation theology, which is oppressor-and-victim” and “people aren’t recognizing his version of Christianity.”
I take Beck to be using the word “recognize” in its ordinary “perceptive” sense (as in, he didn’t recognize his long-lost childhood friend). This is to be distinguished from “recognizing” in the sense of formal acknowledgement (as in, the U.S. refused to recognize the new, breakaway Republic in Central Africa).
Obama’s problem is that the Christianity of Rev. Wright, whose congregation he attended for 20 years, and of less abrasive liberation theologists as well, just isn’t recognizable to a great many Americans as Christianity because it doesn’t much resemble the Christianity they are familiar with. If Obama lived in El Salvador, where liberation theology is more common, his Christianity would be less in doubt.
Beck himself, I believe, stands in a slightly different position than most Americans who can’t say Obama is a Christian. Beck recognizes Obama’s religion as a set of beliefs whose adherents call themselves Christians. But Beck does not acknowledge that this belief set actually is Christian. Accordingly, Beck isn’t scratching his head about Obama’s religious stance, but many Americans are.
I’ll leave to others the debate about whether liberation theology should be considered Christian. But I think Beck has put his finger on the reason why so many Americans don’t perceive Obama to be a Christian.